1. Field of the Invention
The present invention relates, in general, to a biodegradable copolyester and, more particularly, to a copolyester copolymerized with an aromatic polyester having a number average molecular weight of not less than 5,000 and an aliphatic polyester biosynthesized by microorganism fermentation. Also,the present invention is concerned with an economical method for preparing the biodegradable copolyester.
2. Description of the Prior Art
Polyester, especially, polyethylene terephthalate has good mechanical properties, chemical resistance, and durability and is useful for various fields of everyday life including substitutes for natural fibers, bottles, plastics and the like. Unlike the natural materials, the polymer, however, has a fatal weakness that it cannot be reduced into nature after use. In other words, synthetic plastics are little or by no means degraded of themselves. Disposable packaging materials, which have sharply been increased in demand, are little reclaimed relative to their tremendous consumption and thus, most of them are wasted. In addition, agricultural film is very difficult to completely regain.
As the environmental pollution caused by the plastics is issued as a serious social problem, many research and development efforts have been directed to biodegradable resins with invoking worldwide interest. In an effort of the protection of environment, degradable resins, which are degraded of themselves after discard, have recently been developed.
Degradable resins are generally grouped into biodegradable resins, which are degraded by microorganisms present in soil, and photodegradable resins, which are degraded by ultra violet ray of day light. When the photodegradable resins are buried in soil, they are hard to degrade because they are little or by no means exposed to the sun. Accordingly, the biodegradable resins are more preferred.
Exemplary biodegradable resins include poly(hydroxyalkanoate) resins, which are synthesized by microorganisms in vivo, and polycaprolactone resins, which are a kind of synthetic polymer.
Such poly(hydroxyalkanoate) resins and polycaprolactone resins are good in biodegradability, but uneconomical due to their high production cost. In addition, the applied physical properties thereof are poor and thus, are low in an aspect of practical value.